Defense Intelligence Reference Document Inertial Electrostatic Confinement Fusion

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In 1997 Miley and his group published
an IEEE paper that summarized their
internal ion injected grid experiments
(Reference 2.3). (As noted earlier "ion
injected" has been used to define the
species forming a potential well. It is not
to be confused with external "gun"
injection where ions form the well, but
are introduced from an external source).
It discusses the discharge physics and
plasma characteristics for various modes
of operation. It explains how the STAR
mode is created by the defocusing
properties concave inward (towards the
center core) in open grid structures.
Indeed the concept is somewhat anti-
intuitive since one might hope for
focusing "optics", but this is not possible
in these configurations. (Indeed various
multi-grid approaches have been studied
with the objective of improving beam
optics for reflection of ions, hence
recirculation. See for example, Reference
2.4. When ions pass through the
concave potential, all but those in the
Figure 2.3. Photograph of a STAR mode discharge.
The "vane" type grid shown 1s only one of a number of
large opening grids designed and used for STAR mode
operation of the neutron source type IEC. This particular
design (but with variations) has been used by the UIUC,
Daimler-Chrysler and Kyoto University. It is rugged,
shows little sputtering and has proven very efficient for
neutron production. Materials used vary from stainless
steel to Mo.
exact center of the curved surface are deflected and lost. The centered ions pass
through to the opposite side and go through the grid opening, then are reflected and
repeat this trajectory. Subsequently ionization events along this path cause a rapid
increase in the recirculating current through the center of the grid openings. This then
produces the beautiful STAR mode discharge shown in Figure 2.3.
The use of a pulsed power supply represents a very important way to study the physics
of high current IECs without employing expensive, very large power supplies and also
avoiding the need for strong cooling to remove the waste heat. The key physics point is
that the beam-beam fusion rate scales as the ion current squared. Most steady state
experiments employ 100s of mA, while pulsing peak values of many amps are possible.
By selecting the pulse width to match or exceed the ion confinement time, typically
order of ms in present devices, a quasi equilibrium is established during the pulse. This
allows study of "equivalent" steady-state physics during the pulse.
Miley's device in Reference 2.6 used a Marx bank technology to provide peak currents
of 10's of amps with a ~0.1 sec width and a low repetition rate (selected to minimize
cooling requirements and also reduce bank recharging requirements).
Another important technology regarding the IEC vessel pumping was developed in the
mid-1990s by staff from Miley's group working at the Idaho National Environmental and
Engineering Laboratory (!NEEL), Idaho with Robert A. Anderl (Reference 2.5). This work
substituted a metallic hybrid getter for the external pumping on the IEC chamber. With
this arrangement, the deuterium is absorbed in the getter material while the vapor
pressure, hence chamber background pressure, is controlled by regulation of the getter
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